1. Field of the Invention
This invention relates generally to contamination control and, more specifically, to contamination control of fluids with media contained in a replaceable assembly.
2. Discussion of Related Art
Many industries require some form of contamination control. Examples include the electronics, aerospace, biotechnology, and the food and beverage industries. Each industry defines an acceptable level of contamination through de facto or formal standards, and these standards typically address particle and gas phase impurities in fluids. Some fields, such as electronics, also effectively define acceptable configuration and physical parameters such as the available footprint in which a purification device should fit and the types and size of plumbing fittings. For example, the semiconductor manufacturing industry is increasingly relying on purification devices having footprints no larger than 3.31 inches on a side.
U.S. Pat. No. 5,558,688 to Cowan et al. (the "'688 patent") and U.S. Pat. No. 5,139,747 to Cato et al. (the "'747 patent") disclose purification systems that may be used in semiconductor manufacturing. The '688 patent, among other things, discloses a purification system having a block body and a one-piece removable canister. The block body interfaces the canister with a gas stream. The canister holds a purification media and includes a tube for carrying the gas from an inlet to the top of the purification media. The gas exits the tube and flows down through the media to an outlet tube, the block body, and eventually the rest of the fluid application system. Each tube has a corresponding wire mesh frit at its distal end relative to the canister's block body. A poppet valve assembly, contained in the canister, isolates the canister from atmosphere during the canisters removal or installation. The '747 patent discloses a one-piece inline purification assembly having a baffle stack for holding a purification media and for defining a flow path. The input and output ports include a poppet valve assembly to isolate the device.
Some disadvantages of the above arrangements include performance, system cost, difficulty in removing and replacing media, and ability to perform leak tests. Performance involves the amount of media per unit area and the ability of a fluid to interact with that media efficiently. The length of the flow path is less than the length of the canister, flowing top to bottom. Any media voids affect performance because fluids will take the path of least resistance in flowing through the assembly. Likewise, the geometry of the flow path affects performance. System cost is affected by component cost of the overall system and the replaceable components and by the labor costs of maintaining the assembly. Maintenance costs are affected by the difficulty in removing and replacing media and in handling the devices. The ability to perform leak tests is self explanatory and a consequence of the design.
Concerning performance, the '688 inlet tube is empty and does not contribute to performance. Some canister areas, e.g., the area below the output tube, contain media but in a position less likely to contribute to performance. These areas are believed to be an inefficient use of valuable space. At least some, if not all, embodiments are believed to be difficult to completely pack with media, producing the possibility of media voids. Moreover, the possibility of media voids may also arise from settling of media, for example, during shipping or handling of the canister.
Concerning cost, the '688 system requires a canister change, and the '747 system requires a complete system change, when the media is exhausted. The replaceable components are costly because they are manufactured with expensive techniques. Given tight configurations of modern systems, the replaceable components are difficult to remove and replace, as they require access to the base of the assemblies, thus increasing maintenance costs. Neither the '688 system nor the '747 system provides explicit mechanisms to leak test an installed system.